1. Field
This invention relates to the art of decreasing the corrosion of ferrous metals and to the art of decreasing the rate of oxidation of aqueous solutions of alkali metal and ammonium sulfites and bisulfites upon exposure to a source of oxygen such as the atmosphere.
2. Prior Art
Over the years many investigators have studied the oxidation of sulfites and the effect of various substances on the oxidation of sulfites. Known catalysts for the reaction are certain heavy metal cations, particularly divalent cobalt, copper, iron, manganese, and nickel. Many chemicals are known to either inhibit or retard the oxidation. These are generally free radical scavengers.
It is well known to use alkali metal and ammonium sulfites and bisulfites, preferably sodium sulfite, as corrosion inhibitors in aqueous systems containing dissolved oxygen which contact ferrous metals. The sulfite reacts with the oxygen to eliminate it from the system thus preventing its reaction with the ferrous metal. Two books which discuss the corrosion of ferrous metals and the use of sulfites for corrosion protection are: Metallic Corrosion Passivity and Protection, Ulick R. Evans, Longmans, Green and Co. (New York), 1946; Corrosion and Corrosion Control, Herbert H. Uhlig, John Wiley and Sons, Inc. (New York), 1963.